Microphone-speaker device

ABSTRACT

A hand-held tape recording device comprising, within a casing, a reversible electro-acoustic transducer serving as both a microphone and a speaker which performs the functions of converting sound waves into electrical signals and electrical signals into sound waves, tape recording means connected to the transducer, and a concave elliptic sound reflector having first and second foci and juxtaposed to the reversible electro-acoustic transducer for directing sound waves to and from the transducer. The reflector has plural radial splits to facilitate variation in curvature thereof, and the device further includes means carried by the casing for moving the center of the reflector in a direction aligned with the axis of the reflector to vary the curvature of the reflector.

United States Patent 1 J insen ji Sept. 23, 1975 Sei Jinsenji, Yokohama,Japan [30] Foreign Application Priority Data Sept. 28, 1971 Japan46-75650 [52] U.S. Cl 179/102; 179/1 MF; 179/179; 181/176 .[51] Int. ClH04r l/00 [58] Field of Search. 179/1 MP, 178, 179, 100.2 Z, 179/102;.181/27 R, 30, 31 A; 340/8 FT;

FOREIGN PATENTS OR APPLICATIONS 371,031 4/1931 United Kingdom 179/1 MFPrimary ExaminerKathleen H. Claffy Assistant ExaminerGeorge G. StellarAttorney, Agent, or FirmCooper, Dunham, Clark, Griffln & Moran [57]ABSTRACT A hand-held tape recording device comprising, within a casing,a reversible electro-acoustic transducer serving as both a microphoneand a speaker which performs the functions of converting sound wavesinto electrical signals and electrical signals into sound waves, taperecording means connected to the transducer, and a concave ellipticsound reflector having first and second foci and juxtaposed to thereversible electro-acoustic transducer for directing sound waves to andfrom the transducer. The reflector has plural radial splits tofacilitate variation in curvature thereof, and the device furtherincludes means carried by the casing for moving the center of thereflector in a direction aligned with the axis of the reflector to varythe curvature of the reflector.

1 Claim, 5 Drawing Figures US Patent Sept. 23,1975 Sheet 1 of2 3,908,095

FIG.2

US Patent Sept. 23,1975 Sheet 2 of2 3,908,095

FIG.4

Q III 1110 u MICROPHONE-SPEAKER DEVICE BACKGROUND OF THE INVENTION Thisinvention relates to a reversible electro-acoustic transducer device ormicrophone-speaker device serving as both a microphone and a speaker.

A reversible electro-acoustic transducer device serving as both amicrophone and a speaker permits the functions of converting electricsignals into sound waves and sound waves into electric signals to beperformed in a single device. Thus, such transducer device offers theadvantage of occupying little space when installed in various equipment.In most cases, the device is used as a speaker concurrently serving as amicrophone.

In recent years, attempts have been made to incorporate a reversibleelectro-acoustic transducer device in various types of equipment for thepurpose of obtaining an overall compact size in a tape recorder andother equipment by taking advantage of its compactness. The tendency touse a reversible electro-acoustic transducer device is particularlymarked in tape recorders of the ultra small size, particularly taperecorders of the portable type which are sometimes referred to asdictating machines. These devices, which are generally operated whilebeing held by hand, have been developed toserve the purpose of recordingapparatus for recording the conversation between persons and the purposeof reproducing apparatus for enabling a single person to hear thereproduced sound.

The equipment of the aformentioned type is preferably of an ultra smallsize. It is preferable to incorporate in such equipment a reversibleelectro-acoustic transducer device serving as both a microphone and aspeaker in order to attain the end of obtaining an overall compact sizein the equipment of the aformentioned type.

Reversible electro-acoustic transducer devices which are available forthe purpose mentioned above can serve as both a microphone and aspeaker, but they are generally much lower in sound conversionefficiency than microphones and loudspeakers which individually performtheir respective functions.

When reversible electro-acoustic transducer devices are incorporated inequipment of an ultra small type, such transducer devices themselvesmust be compact in size. A reduction in the size. of reversibleelectroacoustic transducer devices inevitably has the disadvantage ofmarkedly decreasing their efficiency in performing the functions ofconverting sound waves into electric signals and electric signals intosound waves.

SUMMARY OF THE INVENTION This invention has as its object the provisionof a microphone-speaker device wherein a sound reflecting plate providedwith a curved sound reflecting surface is juxtaposed to a reversibleelectro-acoustic transducer arranged in a position which corresponds toa focus of the sound reflecting surface, so that the sound energyconversion efficiency of the transducer. can be increased andaforementioned disadvantage of the prior art can be eliminated.

The microphone-speaker device according to this invention which isconstructed as aforementioned has a much enhanced sensitivity incollecting sound when used as a microphone and can provide asufficiently high sound pressure energy in the service range forsatisfactory use as a speaker.

More particularly, the invention in specific aspects contemplates theprovision of a concave sound reflector, and transducer means forreceiving and emitting sound mounted at a focus of the reflector, forreflective transmission of sound waves by the reflector between thetransducer and a locality spaced from' the transducer and reflector. Inone embodiment, the reflector is an elliptic reflector; in anotherembodiment, a parabolic sound reflector is used. Means may be providedfor adjusting or varying the curvature of the reflector.

Further features and advantages of the invention will be apparent fromthe detailed description hereinbelow set forth, together with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of oneform of ultra miniature tape recorder;

FIG. 2 is a plan view showing the manner in which the tape recorder ofFIG. 1 is used;

FIG. 3 is a sectional view of a microphone-speaker device comprising oneembodiment of this invention;

FIG. 4 is a sectional view of a modified form of sound reflectingsurface suitable for use in a device of the type shown in FIG. 3; and

FIG. 5 is a sectional view showing one form of means for varying thecurvature of the sound reflecting surface in a device embodying theinvention.

DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION FIG. 1 illustratesan ultra miniature tape recorder I sometimes referred to as a dictatingmachine, in which a micro-cassette 2 (or a mini-cassette) of the size ofa small matchbox (carrying a recording tape) can be detachably inserted.The tape recorder 1 has a built-in small reversible electro-acoustictransducer 3 serving as both a microphone and a speaker and can be setat recording, reproducing and shutoff positions by suitably depressing apushbutton 4. Transducers of this type are known in the art andaccordingly need not b described in detail.

The ultra miniature tape recorder of the aforementioned type isgenerally used in a manner shown in FIG. 2 which is a plan view showinga person H using this equipment. As can be seen from this figure, thespacing between the tape recorder l and the mouth M of the person H issubstantially equal to the spacing between the tape recorder 1 and theear E of the person H, and the spacings can be regarded as having avalue D which is substantially uniform.

This invention is based on the discovery that if a sound reflectingsurface is used advantageously by considering the fact that the value Dis substantially uniform, the ability of the small reversibleelectro-acoustic transducer 3 to collect and produce sound can beincreased so as to increase its sound energy conversion efficiencymarkedly.

FIG. 3 shows the microphone-speaker device comprising one embodiment ofthis invention. It shows in an enlarged sectional view the essentialportions of the device comprising the small reversible electro-acoustictransducer 3 serving as both a microphone and a speaker built in thetape recorder 1. More specifically, the tape recorder l is housed in acasing la which is formed in one portion or front portion thereof withan opening 1b for permitting sound to enter into the casing and radiateout of the casing therethrough. The opening 1b has mounted therein aperforated support plate 5 which is formed therein with a multitude ofperforations 5a.' The small reversible electro acoustic transducer 3serving as both a microphone and a speaker (i.e. for conversion of soundto electrical signals, and vice versa) is mounted on the perforatedsupport plate 5 in a position in which the center of the sound axis ofthe transducer 3 coincides with the center of the opening 1b.

It will be understood that the tape recorder includes means for drivingthe tape within the aforementioned micro-cassette and means forrecording signals on the tape from the transducer 3 and for detectingsignals re- .corded on the tape for conversion to audible sound by thetransducer 3$ all such means may be generally conventional, as will beapparent to those skilled in the art, and are therefore not shown, forsimplicity of illustration.

In accordance with the invention, a sound reflecting plate 6 is attachedto a bottom wall 1c of the casing 1a in facing, spaced relation to thetransducer 3 and includes a concave sound-reflecting surface 6a which iselliptic in shape, opening toward the transducer 3 with the center ofthe sound axis serving as a common center axis of the ellipticreflecting surface 6a. An elliptic sound reflector of the type shown at6 is adapted to reflect sound, emanating from the locality of either oftwo foci F1 and F2 (spaced along axis 0), to the locality of the otherof the two foci. The sound reflecting plate 6 and reversibleelectro-acoustic transducer 3 are disposed in relative positions suchthat the position of a first focus Fl of the sound-reflecting surfacecoincides with the location of a vibration plate 3a of the transducer 3.

By this arrangement, a second focus F2 of the elliptic sound-reflectingsurface 6a will be disposed in a position which is outside the casingla. Thus, if the second focus F2 is used as a sound transmitting andreceiving position for the vibration plate 3a and the spacing betweenthe first focus F1 and the second focus F2 is set at the value D shownin FIG. 2, the sound emanating from the sound transmitting and receivingposition corresponding to the second focus F2 will pass through theperforations 5a as indicated by arrows A and will be reflected by theelliptic sound-reflecting surface 6a to converge on the reversibleelectro-acoustic transducer 3 and cause the vibration plate 3a tovibrate, for conversion of the sound to electrical signals. The soundradiating out of the reversible electro-acoustic transducer 3 will bereflected by the elliptic reflecting surface 6a and pass through theperforations 5a to converge on the second focus F2 as indicated byarrows B. As will be understood, the transducer 3 is oriented to receivesound (for conversion to electrical signals) reflected to focus F1 bysurface 6a, and to emit sound toward surface 6a for reflection to focusF2.

Accordingly, if the position of the second focus F2 is 6 the ellipticsound-reflecting surface 6a will act as a reflector for effectingconvergence of sound waves from that source on reversibleelectro-acoustic transducer 3 when the transducer is made to function asa microphone. Conversely, when the reversible electroacoustic transducer3 is made to act as a speaker, the sound radiating out thereof will bereflected by the elliptic reflecting surface 6a and have a considerablyhigh sound pressure when it reaches the second focus F2 or itsneighborhood. Thus, if a person is positioned at the second focus F2 andlistens to the reproduced sound, the reproduced sound can be heard withadequately high sound pressure.

Preferably, the reversible electro-acoustic transducer 3 which is usedas aforementioned has a dual directivity in order that sound may becollected and radiated. Also, the surface of the reversibleelectro-acoustic transducer 3 which faces the sound-reflecting surface6a is preferably convex, and shaped such that it is rounded as much aspossible so as to preclude scattering of reflected sound waves near thereflecting surface.

Although the sound reflector employed in the devices of the presentinvention is shown in FIG. 3 as elliptic, other configurations ofconcave sound reflectors may be employed, e.g. in the same structuralrelation to other parts of the device as the reflector 6 of FIG. 3. FIG.4 shows another form of the concave soundreflecting surface which is aparabolic sound-reflecting surface 16a as contrasted to the ellipticsoundreflecting surface of FIG. 3. By using the parabolicsound-reflecting surface 16a (i.e. a concave parabolic sound reflectoropening toward the transducer 3) mounted within the casing while placingthe vibration plate of the reversible electro-acoustic transducer 3 at afirst focus F of the reflecting surface 16a, it is possible to causereflected sound waves (from the mouth of a person or other sound sourceexternal to the casing, and directed toward the reflector) to convergeon the transducer 3, thereby permitting the same to function as amicrophone as satisfactorily as described with reference to FIG. 3. Asecond focus of the parabolic reflecting surface shown in FIG. 4 isinfinite, so that the sound radiated out of the reversibleelectro-acoustic transducer (when the transducer is made to function asa speaker) reaches the sound receiving position in the form of parallelsound beams. However, since the radiated sound has a high directivity,it is possible for the transducer to effect sound energy conversionefficiently.

According to this invention, it is possible to adjust the soundemanating and receiving position suitably by varying the curvature ofthe sound-reflecting surface 6a or 16a so as to determine such positionoptimally. FIG. 5 shows means for attaining the end. The soundreflectingplate 6 provided with the elliptic soundreflecting surface 6a is shownin the figure as being formed with a plurality of splits 6b directedradially of the elliptic surface, so as to facilitate variation oradjustment in curvature of the surface. By moving the center of thesound-reflecting plate 6 axially, it is possible to vary the curvatureof the ellipse, i.e. of surface 6a. If the curvature is varied, then theposition of the focus is also varied, so that it is possible to vary thesound-emanating and receiving position optimally.

The means for moving the position of the center of the sound-reflectingplate 6 along the sound axis shown in FIGS comprises an adjusting screw7 threaded into the bottom wall 1c of the casing 1a so that its forwardend may bear against the position of the center of the sound-reflectingplate 6 to move the plate along the sound axis. When the adjusting screw7 is moved outwardly, the curvature of the reflecting plate 6 resting ona supporter 1d is reduced; when it is moved inwardly, the curvature isincreased.

By varying the curvature of the elliptic soundreflecting plate asaforementioned, it is possible to adjust the elliptic sound emanatingand receiving position optimally. In case the sound-reflecting plate orreflector is parabolic in shape, the thickness of the beams of the soundradiated out of the transducer and reflected by the reflector can beincreased by varying the curvature of the sound-reflecting plate.

It is to be understood that the invention is not limited to theparticular form of the curvature varying means shown and describedabove, and that any other suitable means may be used to attain that endwithout deviating from the scope and spirit of the invention.

In the foregoing description, the invention has been described as beingincorporated in an ultra miniature tape recorder. It is to beunderstood, however, that the invention may be incorporated in othertypes of equipment, e.g. dictating machines.

I claim:

1. A hand-held tape recording device comprising a. a casing dimensionedto be held in the human hand, having an opening for passage of soundbetween the interior and exterior of the casing;

b. a concave elliptic sound reflector having first and second foci andmounted within said casing in facing relation to said opening fordirectionally reflecting sound between said first focus and a localityexternal to said casing, said first focus being located within thecasing and said second focus being at said external locality;

c. transducer means for receiving and emitting sound, supported by saidcasing and disposed at said first focus in facing relation to saidreflector for receiving sound entering said casing through said openingfrom said external locality and reflected to said first focus by saidreflector and for emitting sound for reflection by said reflectorthrough said opening to said external locality;

d. tape recording means contained within said casing and connected tosaid transducer means, for recording and reproducing sound; and

e. means for varying the curvature of said reflector, said reflectorhaving plural radial splits to facilitate variation in curvaturethereof, and said curvaturevarying means comprising means carried bysaid casing for moving the center of said reflector in a directionaligned with the axis of said reflector.

1. A hand-held tape recording device comprising a. a casing dimensionedto be held in the human hand, having an opening for passage of soundbetween the interior and exterior of the casing; b. a concave ellipticsound reflector having first and second foci and mounted within saidcasing in facing relation to said opening for directionally reflectingsound between said first focus and a locality external to said casing,said first focus being located within the casing and said second focusbeing at said external locality; c. transducer means for receiving andemitting sound, supported by said casing and disposed at said firstfocus in facing relation to said reflector for receiving sound enteringsaid casing through said opening from said external locality andreflected to said first focus by said reflector and for emitting soundfor reflection by said reflector through said opening to said externallocality; d. tape recording means contained within said casing andconnected to said transducer means, for recording and reproducing sound;and e. means for varying the curvature of said reflector, said reflectorhaving plural radial splits to facilitate variation in curvaturethereof, and said curvature-varying means comprising means carried bysaid casing for moving the center of said reflector in a directionaligned with the axis of said reflector.